The present invention relates to the field of detectors designed for detecting non-authorized objects in a zone having protected access.
1. Field of the Invention
The present invention applies in particular to detecting non-authorized substances such as drugs.
2. Description of Related Art
Nowadays it is found to be necessary to check with a very high degree of reliability for attempts at introducing or removing non-authorized objects into or from a sensitive zone.
When posed in this way, the problem covers a very wide range of situations, and in particular but in non-limiting manner, it covers detecting objects stolen from chemical firms, customs warehouses, and attempts at introducing dangerous objects into protected zones such as schools, and public or private organizations.
Numerous means have already been proposed for performing such detection.
In particular, numerous substance detectors have already been proposed.
Those detectors are based on two possible techniques: trace detection or bulk detection.
The term “trace” refers to both vapor and particulate sampling of the substance.
Trace detectors are considered as passive systems in that they only detect the vapors or microscopic particles emitted from the non-authorized substance. Those systems have a basic physical limitation in the fact that if the non-authorized substance is well packed and the package has been properly cleaned, it doesn't releases any trace and the detection is not possible.
Bulk detectors, which use a source of radiation (x-rays, gamma rays, radio frequencies, or magnetic field) to stimulate a response from non-authorized substances, are considered as active systems. Different bulk detectors using different detection techniques such as NMR (Nuclear Magnetic Resonance) or NQR (Nuclear Quadrupole Resonance) will be able to detect different categories of substance.
Examples of known substance detectors, and in particular bulk detectors are to be found in the following documents: U.S. Pat. No. 5,206,592, U.S. Pat. No. 5,365,171, U.S. Pat. No. 5,420,905, U.S. Pat. No. 5,592,083, U.S. Pat. No. 6,166,541, U.S. Pat. No. 6,392,408, U.S. Pat. No. 6,489,872, WO-3 076 952.
Moreover, it is found nowadays that people attempting to remove substances fraudulently from a protected zone, a thief stealing from a warehouses, or people attempting to introduce prohibited substances, e.g. a school child attempting to introduce drugs into a school, are making ever-increasing use of shoes and/or socks for hiding the substance in question.
This phenomenon seems to be due essentially to the fact that this zone of the human body is not easy to inspect visually or by touch or by other current inspection means.
On some sensitive sites it is nowadays necessary to make use of X-ray inspection apparatus, thus requiring people leaving the site or entering the site to remove their shoes, since X-rays devices cannot be used directly on shoes that are still being worn because that would lead to exposing parts of the human body to ionizing radiation.